create or replace procedure insert_sale(c_id in NUMBER, imei in NUMBER, sell_date in DATE,e_id in number) is

BEGIN
    if sell_date is not null then
		INSERT INTO SALES(CUSTOMER_ID,PRODUCT_IMEI_NO,DATE_OF_SALE,EMPLOYEE_ID) values(c_id, imei, sell_date, e_id) ;
		else
		INSERT INTO SALES(CUSTOMER_ID,PRODUCT_IMEI_NO,EMPLOYEE_ID) values(c_id, imei, e_id) ;
		end if ;
END;